The present invention relates to a method and an apparatus for processing wafers, e.g., semiconductor wafers, utilizing a wafer processing disk.
A microchip or integrated circuit formed on a wafer surface must be separated from the wafer surface, which typically contains an array of integrated circuits, and put in a protective package. Semiconductor wafer packaging has traditionally lagged behind wafer fabrication in process sophistication and manufacturing demands. The advent of the VLSI-ULSI era in chip density has forced a radical upgrading of chip packaging technology and production automation. It is a widely held belief in the art that eventually packaging will be the limiting factor on the growth of chip size. Accordingly, much effort is going into new package designs, new material development, and faster and more reliable packaging processes.
It is often necessary to thin wafers in the packaging process because of an industry trend to using thicker wafers in fabrication. This trend presents several problems in the packaging process. Thicker wafers require the more expensive complete saw-through method at die separation. Thicker wafers also require deeper die attach cavities, resulting in a more expensive package. Both of these undesirable results are avoided by thinning the wafers before die separation. It is also often necessary to remove, by wafer thinning, electrical junctions formed inadvertently on the back side of the wafer during fabrication.
Thinning steps generally take place between wafer sort and die separation. Wafers are reduced to a thickness of 0.2-0.5 mm. Thinning is done through mechanical grinding, mechanical polishing, or chemical-mechanical polishing. Wafer thinning or backgrinding has traditionally been a difficult process. In backgrinding there is the concern of scratching the front of the wafer and of wafer breakage. Stresses induced in the wafer by the grinding and polishing processes must be controlled to prevent heat induced wafer and die warping. Frequently, to secure a wafer 22 during a thinning operation, the wafer 22 is secured to a wafer chuck 26 with an adhesive sheet or film 24, see FIG. 10. However, heat generated during the thinning process subjects the adhesive sheet or film 24 to degradation and failure resulting in wafer damage. Accordingly, there is a need for a wafer processing apparatus that minimizes heat induced stress and damage during wafer thinning.
Wafer thinning done through mechanical grinding, mechanical polishing, or chemical-mechanical polishing often requires a plurality of wafer polishing or grinding disks to achieve a desired outcome. For example, it is often necessary to initiate wafer processing with a coarse grinding disk and complete the processing with a fine grinding disk. This requirement leads to corresponding increases in production time and equipment cost. Accordingly, there is a need for a wafer processing method wherein a single processing disk may be utilized where conventional methods utilize a series of processing disks.